Superconducting devices, such as resonator devices, are used in versatile applications such as high-frequency filters, photon detection in astrophysics research, and quantum bits (“qubits”) for quantum computing. The success of these applications often requires low-loss operation of the resonators, especially in quantum computing. The quest for materials that have low loss in RF resonant structures at low temperatures is an area of great interest for quantum computation and photon detection. Indeed, low loss, i.e., high quality factor, in these applications is necessary to have long resonant lifetimes at low power, and well-resolved frequencies and low noise at high power Important examples are the storage of arbitrary quantum states in superconducting resonators at very low fields, i.e., in the single photon regime where the electric field is much less than the critical field, and multiplexed readout of kinetic inductance photon detectors.
Superconducting materials such as Al, Re, and Nb on crystalline substrates such as silicon and sapphire are capable of producing low internal loss, δi, and therefore high internal quality factors
  (            Q      i        =          1              δ        i              )of approximately 105-106 in a high field regime. However, when restricted to low field levels such as used in superconducting quantum information applications, quality factors are reduced to the 104-105 range. This limits reproducible lifetimes, τ=Q/2πf, to be approximately 1 μs when operated in the 1-10 GHz range. It is well accepted that parasitic two-level systems (TLS) in oxides at surfaces, interfaces, and dielectrics contribute predominantly to the losses in these structures. Nitrides, on the other hand, are very stable, especially against oxidation.
Despite the significant progress that has been made towards understanding various loss mechanisms, materials properties have not been used to optimize the performance (e.g., minimize the loss) of a superconducting resonator.